Nonsuicidal self-injury (NSSI) is a widespread mental health concern among students in university (Swannell et al., 2014). Stressful experiences in university may lead to increased risk for NSSI by undermining an individual’s ability to cope with distress. However, longitudinal examinations of the link between stressful experiences in university and NSSI, and the mechanism driving the association, are lacking. The current study investigated the process through which stressful experiences may heighten risk for NSSI in a sample of 1132 undergraduate students (70% female, mage = 19.11). Participants reported on daily stressors in university, difficulties in emotion regulation, and NSSI each year for three consecutive years. Path analysis revealed a significant indirect effect from stressful experiences to NSSI through emotion regulation. This association was bidirectional; greater frequency of NSSI predicted increased risk for stressful experiences through emotion regulation. Theoretical and practical implications are discussed.